Similar to the term "noob", scrub is generally used as an insult, although whereas noob refers to a new player with a poor understanding of the game, scrub primarily refers to a sore loser who chooses to complain about other peoples' decks rather than try to improve their own. Thus, a bad player can be both a scrub and a noob, a scrub but not a noob, or a noob but not a scrub. However, in practice many players do not distinguish between noob and scrub, using the terms interchangeably.
Certain behaviours mark out a player as a scrub. They will often complain that a specific card, combo or aspect of the game, such as land destruction or counter-magic, is "cheap" or unfair. In casual play they may go so far as to refuse to play against decks using a strategy they dislike, while in tournaments they may automatically concede at the first sign of such a deck. Scrubs also typically refuse to listen to advice from more experienced players over how to improve their deck, arguing that an objectively poor card choice or deck strategy is worthwhile. As a result, scrubs in tournament play are seen as an annoyance, although their lack of skill generally means they do not pose a threat to better players.
As scrub has a clearly negative meaning, it is commonly used (particularly online) as an insult to refer to casual players or anyone with limited tournament experience, regardless of whether that person is a "true" scrub.